The invention concerns rotation-impairing drive unit for rotating a data carrier having a brushless d.c. motor with a permanent-magnet rotor, and a stator having a winding, the winding being formed by one or plural winding coils, a circuit arrangement for controlling the energization of the winding to generate a magnetic field effecting rotary motion of the rotor, and also a reading arrangement for reading signals recorded on the data carrier.
For driving daft carriers such as computer data-storage planers use is generally made of a brushless d.c. motor, with a data-carrier-receiving hub preferably being secured directly a the motor""s shaft, so that the data carrier be directly driven. In order to assure a reliable, error-free reading of the data signals despite high daft recording density, it is necessary to drive the data carrier at a high speed that is uniform; for this purpose, as exact as possible a switchover (commutation of the current fed to the d.c. motor""s stator-winding coils is necessary. For this purpose, known d.c. motors have one or plural sensors (e.g. Hall elements) inside the motor, housing in the immediate vicinity of the region of the rotor""s magnetic influence, and these are caused to issue signals as a result of the alternation of the magnet field during rotor rotation. A circuit board likewise arranged in the motor housing carries the components of a circuit, to which the sensor output signals are fed, and by means of which commutation of the current for the winding is performed in correspondence thereto.
With drive units for data carriers, a further requirement is that their structural height be as low as possible and this, in the case of d.c. motors of the direct-drive type, basically meaning the axial length or the motor""s structure. A manufacturer of such motors therefore must make every effort and adopt every reasonable expedient that would serve to reduce axial height. In addition, there is for the motor manufacturer the always present goal, to be able to make and sell the motor at low cost.
An object of the invention isto more advantageously design, and also simplify the construction of, data-carrier-rotating drive units of the type incorporating a brushless d.c. motor, while simultaneously achieving improved commutation of the motor winding.
In accordance with the invention this object is achieved as follows: the output of the reading arrangement is connected with the circuit arrangement that controls the amortization of the stator winding; and the data carrier has control signals which characterize at least those angular positions of the rotor relative to the stator at which the switchover (commutation) of the current fed to the winding coils is to be initiated.
Further particulars of the invention may be had from the description of several exemplary embodiments.
The advantage of the invention resides in particular in the fact that, by using components that are anyway present in a data-storage unit of the type here in question, one can entirely eliminate the sensor structure that in prior art was conventionally provided internal to the motor, and can furthermore eliminate the associated circuitry and circuit board. As there no longer needed components were arranged in the motor housing at an axial end thereof, it becomes possible to shorten the axial length of the motor correspondingly. At the same time, one eliminates problems associated with the need to connect inside the motor housing, a perhaps rather high number of coil ends to a circuit. Further, there no longer arises the particularly critical problem of the heating up of electronic components within the interior of the motor housing, which is closed and heats up as a result of the heating-up of the winding.
The to the relatively large data carrier diameter and high resolution or the recorded signals, very exact angular positioning of the commutation-control signals can be realized. Also, and without added cost, plural signals can be provided for each time of switchover in the supply of current to the winding, so that e.g. speed-regulating units effective during small amounts of angular motion can be provided, such that immediate corrective adjustment of the supply of energizing current to the winding become possible. Such speed-regulating units, when used in conjunction with sets of desired-speed data, make possible the implementation of speed profiles, for example acceleration and deceleration profiles.
Exemplary embodiments of the invention was illustrated in the drawings and are described in greater detail below.